Saliva diagnostics - Current views and directions

Abstract

In this review, we provide an update on the current and future applications of saliva for diagnostic purposes. There are many advantages of using saliva as a biofluid. Its collection is fast, easy, inexpensive, and non-invasive. In addition, saliva, as a "mirror of the body," can reflect the physiological and pathological state of the body. Therefore, it serves as a diagnostic and monitoring tool in many fields of science such as medicine, dentistry, and pharmacotherapy. Introduced in 2008, the term "Salivaomics" aimed to highlight the rapid development of knowledge about various "omics" constituents of saliva, including: proteome, transcriptome, micro-RNA, metabolome, and microbiome. In the last few years, researchers have developed new technologies and validated a wide range of salivary biomarkers that will soon make the use of saliva a clinical reality. However, a great need still exists for convenient and accurate point-of-care devices that can serve as a non-invasive diagnostic tool. In addition, there is an urgent need to decipher the scientific rationale and mechanisms that convey systemic diseases to saliva. Another promising technology called liquid biopsy enables detection of circulating tumor cells (CTCs) and fragments of tumor DNA in saliva, thus enabling non-invasive early detection of various cancers. The newly developed technology-electric field-induced release and measurement (EFIRM) provides near perfect detection of actionable mutations in lung cancer patients. These recent advances widened the salivary diagnostic approach from the oral cavity to the whole physiological system, and thus point towards a promising future of salivary diagnostics for personalized individual medicine applications including clinical decisions and post-treatment outcome predictions. Impact statement The purpose of this mini-review is to make an update about the present and future applications of saliva as a diagnostic biofluid in many fields of science such as dentistry, medicine and pharmacotherapy. Using saliva as a fluid for diagnostic purposes would be a huge breakthrough for both patients and healthcare providers since saliva collection is easy, non-invasive and inexpensive. We will go through the current main diagnostic applications of saliva, and provide a highlight on the emerging, newly developing technologies and tools for cancer screening, detection and monitoring.

Keywords: Saliva; biomarkers; diagnostics; liquid biopsy; point-of-care; trancriptomics.

Figure 1

Major areas of salivary diagnostics. (A color version of this figure is available in the online journal.)

Figure 2

Oral squamous cell carcinoma in the right buccal mucosa of a 50-year-old female patient. Since the lesion was asymptomatic, the patient did not seek for medical consultation earlier and the cancer was diagnosed during a regular check-up appointment. Early diagnosis is preferable due to tendency of the tumor to spread. (A color version of this figure is available in the online journal.)

Figure 3

55-year-old female patient with xerostomia, xeroftalmia, and non-tumoral, non-inflammatory bilateral enlargement of the parotid gland diagnosed as Sjögren's syndrome. (A color version of this figure is available in the online journal.)

Figure 4

Electric field-induced release and measurement (EFIRM) technology for the detection of epidermal growth factor receptor (EGFR) mutations in bodily fluids of patients with lung cancer. (reproduction from Wei et al.). (A color version of this figure is available in the online journal.)